1. Field of the Invention
This invention relates in general to the manufacture of magnetic sensors, and more particularly to method for providing a liftoff process using a single layer resist and chemical mechanical polishing and sensor formed therewith.
2. Description of Related Art
Magnetoresistive (MR) read transducers are employed extensively for reading magnetically recorded data, typically recorded in parallel tracks on magnetic disk or on magnetic tape. Anistropic magnetoresistive (AMR) heads are one type of magnetoresistive head and include an AMR sensor contacted by longitudinal bias and conductor leads films. Typically, the AMR sensor and bias and conductor films are sandwiched between inductive write films, or between an inductive write film and a shield.
The AMR sensor typically includes a ferromagnetic sense layer separated by a nonmagnetic spacer layer from a ferromagnetic reference layer. The reference layer generates a transverse bias reference field, either by activation from the current supplied to the sensor for sensing the resistance of the sense layer, or by being pinned in a transverse direction through exchange coupling between the reference layer and an underlying ferromagnetic pinning layer. The transverse bias is conventionally used to maintain the sensor in its most linear operating range.
Longitudinal bias is conventionally required to reduce Barkhausen noise for the stabilization of MR sensors. Two major types of longitudinal bias are currently utilized, the overlaid longitudinal bias wherein separate longitudinal bias layers overlay the sense layer in each of the end regions, and the abutting longitudinal bias wherein the sense layer is only in the center region and the bias layers abut and are adjacent the sense layer in the end regions.
Another magnetoresistive head gaining in usage is the giant magnetoresistive sensor (GMR), which employs pinned and free ferromagnetic layers separated by a thin film layer of nonmagnetic material. The voltage across the GMR sensor is related to the rotation of the magnetization in the free ferromagnetic layer as a function of the magnetic field being sensed. Although the mechanism for sensing the magnetic field of the data being sensed is different from the magnetoresistive effect of the AMR sensor, the GMR sensor must also be stabilized by a longitudinal bias field. Typically, the GMR sensor is stabilized by overlaid longitudinal bias layers at each end of the sensor, although abutting longitudinal bias is also employed.
Magnetic head assemblies are typically made of multiple thin film layers, which are patterned to form various shaped layers in the head. Some of the layers are plated while other layers are sputter deposited on a wafer substrate. The read head portion of a magnetic head assembly includes multiple layers that are typically sputter deposited. For example, the multiple layers of a read sensor, hard bias and lead layers connected to the sensor and first and second read gap layers below and on top of the sensor are typically sputter deposited.
The longitudinal bias layers are conventionally overlaid with conductors, which comprise the conductor, leads at each end of the sensor. A current is supplied between the conductors which is conducted by the longitudinal bias layers to each end of the sense layer(s) and the voltage generated by the current across a central region of the sense layer(s) between the bias layers is the sense signal representative of the sensed recorded data. Thus, the active width of sense layer is defined by the central region between the longitudinal bias layers at each end of the sense layer central region.
A key dimension for MR transducers is the width of the active sense region, which defines the trackwidth of the recorded data that is read. If the active sense region width is narrower and more precisely defined, the data tracks of recorded data may be narrower and closer together, thereby allowing more tracks on the same dimensioned recording media and thereby increasing the data capacity of the recording media.
The read head portion of a magnetic head assembly, which includes multiple layers, is typically formed using sputter deposition techniques. For example, the multiple layers of a read sensor, hard bias and lead layers connected to the sensor and first and second read gap layers below and on top of the sensor are typically sputter deposited. For example, a full film layer of the required material may be sputter deposited on a wafer substrate. A patterned photoresist layer is formed on the layer and the exposed portion of the layer is ion-milled away. Then, the photoresist layer is removed leaving the desired shaped layer that was protected therebelow.
This method of shaping sputter deposited layers has been generally superseded by a bilayer lift-off mask scheme. The bilayer lift-off mask is employed for the purpose of making contiguous junctions of the first and second lead layers with first and second side edges respectively of the read sensor. Multiple read sensor layers are sputter deposited in full film on the wafer substrate followed by formation of the bilayer lift-off mask covering a read sensor site. Ion milling is then employed to remove all of the read sensor material except that below the mask. Full films of hard bias and lead layer materials are then sputter deposited which cover the top of the lift-off mask and an area surrounding the lift-off mask.
It is important that the height of the undercuts be greater than the thickness of the hard bias and lead layers. This is so a photoresist stripper can reach the bottom release layer. The stripper is then introduced which dissolves the bottom release layer causing the bilayer lift-off mask and the hard bias and lead materials deposited thereon to be released from the wafer substrate leaving the aforementioned contiguous junctions between the first and second lead layers and the first and second side edges respectively of the read sensor.
The bilayer lift-off mask scheme has significantly improved the making of read heads by forming contiguous junctions between the lead layers and the read sensor. Less processing steps are required and the profile of the lead and hard bias layers above the read sensor has been reduced. Unfortunately, bilayer lift-off masks limit the track width of read heads. The more narrow the track width the greater the tracks per inch (TPI) that can be read by the read head from a rotating magnetic disk. Accordingly, the greater the tracks per inch the greater the storage capacity of a disk drive employing such a read head.
Theoretical drawings of MR heads indicate that the edges of the longitudinal bias layers and the leads are perfectly aligned and perfectly vertical, either in the overlaid longitudinal bias or the abutting longitudinal bias. However, current processing control of the length and height of the undercut has not been precise enough for current track widths goals. Conventional manufacturing produces edges that are less than perfectly aligned and less than perfectly vertical. Long first and second undercuts leave insufficient release layer material which can cause the bilayer lift-off mask to be separated from the substrate or topple over during subsequent processing steps of ion milling and sputter deposition. If the undercut is too short fencing can occur. Fencing is deposition of the sputtered material across the height of the undercut.
In a mass production environment, the design of the disk file must accommodate the various active areas of MR read transducers. Therefore, the more difficult it is to align the edges, the more difficult it is to define the width of the active sense region, and the parallel tracks of recorded data must be located further apart to accommodate the various widths of the active sense region of the manufactured transducers. Also, the ion-milling process required with bilayer liftoff mask attacks the tip photoresist layer and thereby reduces its width.
It can be seen that there is a need for a method for providing a liftoff process using a single layer resist and chemical mechanical polishing and sensor formed therewith.